1. Field of the Invention
The present invention relates to a magnetic recording medium, such as a magnetic tape, which can accept high density recording, has a high reproduction output and excellent running stability.
2. Description of the Related Art
A variety of magnetic recording media, such as magnetic tapes (e.g., a video tape) and magnetic disks for computer memories, have been in use. The demand for high performance of these magnetic recording media, particularly the demand for high recording density and running durability has been increasing from year to year.
An increase in recording density is achieved by a reduction in recording wavelength, which can result in insufficient reproduction output. In order to maintain a sufficient output level, it has been proposed to adopt a multilayer structure in which an intermediate layer for improving electromagnetic conversion characteristics is provided under a magnetic layer.
It is essential that the track of a magnetic recording medium in contact with a magnetic head should be stable during running in order to obtain stable output during running. For this purpose it is desirable for the tape to run stably.
In order to obtain a high output in a stable manner in a high-density magnetic recording medium, it has been a practice to provide a recording layer having a multilayer structure and to make the surface of the magnetic layer smooth, i.e., to reduce the surface roughness. However, today's increased recording density has made it more difficult to obtain a sufficiently high output by applying conventional techniques. Further, a mere improvement in surface smoothness causes an increase in the coefficient of friction between a magnetic head and the recording medium, and sticking can occur between them, which impairs running stability.
Related art concerning the surface roughness of a magnetic layer or a backcoating layer in a magnetic recording medium is found in Japanese Patent Laid-Open No. 1914/92 and U.S. Pat. No. 5,547,772. The former discloses a magnetic recording medium having a magnetic layer whose surface roughness is 6 nm or less and a backcoating layer whose surface roughness is 8 nm or less, the backcoating layer having 500 to 5000 projections having a height of 0.05 to 0.8 .mu.m per mm.sup.2. The magnetic recording medium disclosed is not deemed suitable for high-density recording because the magnetic layer is as thick as 3 .mu.m and the total medium is as thick as 13.5 .mu.m. In addition, there is no mention of the molecular orientation ratio of the substrate and the skewness of the magnetic layer and the backcoating layer, as well as no mention of the influences of the molecular orientation ratio and skewness upon the wobbling of a magnetic recording medium in the width direction during running.
U.S. Pat. No. 5,547,772 discloses a magnetic recording medium in which the magnetic layer has a thickness of 1.2 .mu.m or smaller and a surface roughness of 0.006 .mu.m or less. U.S. patent also does not refer to the molecular orientation ratio of the substrate and the skewness of the magnetic layer and backcoating layer, and also does not refer to the influences of these factors on the wobbling of a magnetic recording medium in the width direction during running.